Pressure compensated pump

ABSTRACT

A control circuit for regulating the output of a variable displacement pump in response to the total demand called for by a plurality of manually operable fluid motor control valves. Each motor control valve has an associated flow control valve connected in series with it. The flow control valves are connected in series with each other, each dividing the flow which is receives between its associated motor control valve and the next downstream flow control valve. The flow division at each flow control valve is responsive to the demand and flow rate across its associated motor control valve, with each flow control valve reducing the flow apportioned to the next downstream flow control valve when its associated motor control valve demands a greater flow than it is receiving. The flow rate diverted by the last of the flow control valves away from its associated motor control valve is thus inversely proportional to the total demand of all the motor control valves, and is sensed by an orifice which produces a signal to increase pump displacement from its normal minimum condition when the total demand exceeds the pump output.

United States Patent [1 Partly Feb.4, 1975 PRESSURE COMPENSATED PUMP[75] Inventor: Paul J. Purdy, Eldridge, Iowa [73] Assignee: J. I. CaseLimted, Racine, Wis.

[22] Filed: July 11,1973

[21] Appl. No.: 378,358

Primary ExaminerEdgar W. Geoghegan Attorney, Agent, or FirmCullen,Settle, Sloman & Cantor [57] ABSTRACT A control circuit for regulatingthe output of a variable displacement pump in response to the totaldemand called for by a plurality of manually operable fluid motorcontrol valves. Each motor control valve has an associated flow controlvalve connected in series with it. The flow control valves are connectedin series with each other, each dividing the flow which is receivesbetween its associated motor control valve and the next downstream flowcontrol valve The flow division at each flow control valve is responsiveto the demand and flow rate across its associated motor control valve,with each flow control valve reducing the flow apportioned to the nextdownstream flow control valve when its associated motor control valvedemands a greater flow than it is receiving. The How rate diverted bythe last of the flow control valves away from its associated motorcontrol valve is thus inversely proportional to the total demand of allthe motor control valves, and is sensed by an orifice which produces asignal to increase pump displacement from its normal minimum conditionwhen the total demand exceeds the pump output.

2 Claims, 2 Drawing Figures PATENTED 5 SHEET 10F 2 PATENTEI] F EB 4 I975SHEET 2 OF 2 VALVE I6 8.

FROM PUMP.

PRESSURE COM PENSATED PUMP BACKGROUND OF INVENTION It is often desirablein hydraulically operated apparatus to utilize a variable displacementpump in conjunction with automatic displacement-controlling means sothat the output of the pump can be maintained at a minimum except whenfurther output is demanded by the system. The advantages of a system soequipped include reduction in horsepower required to operate thecircuit, reduction in heat rise of the fluid when operating in a neutralor low demand condition, possible elimination or reduction in capacityof an oil cooler, and reduction in pump and relief valve noise in lowdemand conditions.

Furthermore. occasions sometimes arise in systems having several fluidmotors receiving the output of the pump that the total demand of thesystem may exceed the capacity of the pump. In such a situation, it maybe desirable to provide means for establishing a priority among thevarious fluid motors. to assure that high priority motors receive thefull fluid flow demanded, even if at the expense of the supply to theother fluid motors. One type of equipment that might require suchfeatures would be earth moving equipment, such as a bulldozer or abackhoe having multiple independently controlled fluid motors forangling, lifting or otherwise positioning the implement.

Circuits having the displacement controlling feature and the priorityestablishing feature are known in the art. An example of such a circuitis disclosed in U.S. Pat. No. 2,892,3l l ofJune 30, I959. Onedisadvantage of the system disclosed in Van Gerpen is that it isincapable of summing the combined fluid demand for the several fluidmotors, it being only capable of sensing the demand in the one motorcalling for the greatest quantity of fluid.

Accordingly, it is the principle object of this invention to provide animproved circuit for controlling the output of the variable displacementpump, which control continuously senses and responds to the combineddemand of all fluid motors in the system, while simultaneously providinga predetermined priority among the various fluid motors if the totaldemand exceeds the output of the pump at any given time.

This and other objects of the present invention will become furtherapparent from the following specification, of which the followingdrawing form a part.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 schematically illustrates apreferred hydraulic circuit incorporating the present invention.

FIG. 2 is a cross-section through a typical manual control valve andflow control valve associated with one of the fluid motors of FIG. I.

DETAILED DESCRIPTION OF THE INVENTION Referring in particular to FIG. Iof the drawings, the improved pump control circuit of this inventiongenerally comprises a variable displacement pump 10, which may be of theswash plate type, three double-acting hydraulic motors 12a, 12b and 12c,each having an associated manual control valve 14a, 14b and 14c, and anassociated flow control valve 16a, 16b and 160, respectively.

The displacement of the pump is under the control of a double-actingpump regulating motor 18, pump demand valve 20 and demand sensingorifice 22.

Pump output line 24 branches to supply the series connected flow controlvalves 16a, 16b and 16c by series-connected supply lines 26a, 26b and260, respectively. Another branch 28 of pump output line 24 suppliesfluid to pump demand valve 20. A return line 30 carries fluid from flowcontrol valve 16: to exhaust, after passing through demand sensingorifice 22.

Each of the flow control valves 16a, l6b and l6c are identical. as areeach of the manual control valves I4a, 14b and 14c. Accordingly, onlythe structure, function and interaction of hydraulic motor 12a. manualcontrol valve and flow control valve 16a need be described, it beingunderstood that the correspondingly numbered elements have identicalconstruction and operation.

Referring now to both FIGS. 1 and FIG. 2, flow control valve continuallymeters and apportions the fluid from supply line 26a to motor supplyline 32 and supply line 26b for the downstream flow control valve 16b.Manual control valve 140 is a conventional four way valve which controlsfluid flow between supply line 32, motor exhaust line 34 and the twomotor lines 36, 38.

Feedback signal lines 40 and 42 act upon the opposite ends of spool 44of flow control valve 160, function along with spring 46 to control thesetting of that valve in response to the setting of and flow throughmanual control valve 14a, as will be described below. A stop 48 limitsthe leftward stroke of spool 44, so that the chamher at the left end ofspool 44 is always in communica tion with line 32 via line 40. Whenspool 54 is in its illustrated neutral position, fluid displaced fromthe chamber at the right end of spool 44 by a rightward stroke of spool44 can bleed off to exhaust 34 via restricted line 50 and annular groove52 of spool 54.

Four-way manual control valve 14a has a spool 54 which controls ports56, 58 and 60. In the neutral position shown in FIG. 2, spool 54 blocksflow from motor supply line 32 through port 56, so that no pressurizingfluid is applied to either motor line 36 or 38. When spool 54 is movedto the right, communication is established across it between motorsupply line 32 and port 56, and the pressure in such line is sufficientto open load check valve 62. Fluid continues to flow from there throughport 58, past spool 54 and out through motor line 36 to the left chamberof hydraulic motor 12a. Thus, rightward movement of spool 54 of manualcon trol valve 14a causes the rod of hydraulic motor 12a to retract,while the righthand chamber of motor 12a exhausts via motor line 38,spool 54 and exhaust line 34.

Similarly, if spool 54 is shifted to the left, flow is again establishedfrom motor supply line 32 through ports 56 and load check valve 62, butthis time it continues through port 60 to motor line 38 to pressurizethe righthand chamber of hydraulic motor 12a, causing extension of therod of that motor. The lefthand motor chamber is then exhausted via line36, spool 54 and exhaust line 34. The function of load check valve 62 isto prevent reverse flow or loss of fluid pressurization in hydraulicmotor 12a if the load exceeds the pressure of the incoming fluid frommotor supply line 32 and port 56.

The fluid diverted from supply line 26a to supply line 26b by flowcontrol valve 160 then enters flow control valve 16b, in the samefashion as supply line 26a enters flow control valve 16a. There, it isidentically apportioned between the motor supply line leading from flowcontrol valve 16b to manual control valve 14b and suppiy line 26cleading to flow control valve 160. Similarly, flow control valve 16capportions the incoming fluid from line 26c between its associatedmanual control valve 14c and supply return line 30 leading to demandsensing orifice 22 and exhaust.

Orifice 22, as will be further explained below, senses the demand of thesystem by sensing the flow rate through it. Upstream and downstreampilot signal lines 64, 66, respectively, carry the pressure signals fromthe respective sides oforifice 22 to the right and left chambersassociated with demand valve piston 68 of demand valve 20. The positionof piston 68, along with associated biasing springs, controls thesetting of the conventional four way pump demand valve 20 to supplyfluid to pump regulating motor 18, where the position of mg 'ulatingcylinder piston 70 controls the setting of swash plate arm 72. In thisfashion, pressure drop across orifice 22 controls the displacement ofpump 10, as will now be further explained.

OPERATION Assume that all manual control valves 14a, 14b and Me are inthe neutral position shown in FIG. 2, so that no fluid is supplied toany of the associated hydraulic motors 12a, 12b or 120. In thiscondition, spool 44 of flow control valve 16a will also be in theposition shown in FIG. 2, wherein communication is established betweensupply line 26a and motor supply line 32, as well as between supplylines 26a and 26b. However, because motor control valve 14a is in itsneutral position, there will be no actual flow through line 32. Thepressure in line 32 will be transmitted through feedback signal line 40and the passage within spool 44 to the chamber at the left end of spool44 and will produce a pressure in opposition to spring 46 to assure thatflow will occur from supply line 26a to supply line 26b.

In this illustrated condition, with no flow across spool 54 to port 56or to feedback signal line 42, there will be a relatively high flow rateinto line 26b, since none of the flow from 260 will be diverted to line32.

Similarly, since motor control valves 14b and 14c are also in theirneutral positions, the spools of flow control valve 16b and 16c will bein the same relative position as spool 44 of flow control valve 16a.Therefore, the flow in line 26b will continue downstream through valves16b and 16c to line and demand sensing orifice 22, without reduction involume.

Accordingly, the illustrated zero demand condition corresponds with ahigh flow rate through demand sensing orifice 22. This high flow ratewill create a high pressure differential in pilot signal lines 64 and66, causing piston 68 of pump demand valve 20 to stroke to the left,which in turn will cause fluid to be supplied from line 28 to therighthand chamber of pump regulating motor 18. The resulting retractionof the rod of that motor will pivot swash plate arm 72 in a pump outputreducing direction, appropriate for this minimum demand condition. Insuch condition, the output of the pump may, for example, be 5% to lgallon per minute in a pump having a capacity of S0 to 100 gallons perminute. This flow rate is sufficient to assure operation of the pumpoutput regulating circuit.

When manual control valve [4a is shifted either to the left or right toproduce extension or retraction of the rod of hydraulic motor 12a, thefluid already avail able in line 32 will begin to flow across spool 54to port 56 and on to the appropriate motor line 36 or 38. A portionofthat flow will also be diverted in the form of a pressure signal tofeedback signal line 42 to oppose the signal already present in feedbacksignal line 40.

Instantaneously with the opening of manual control valve [40, there willbe a drop in pressure in line 32 and feedback signal line 40,accompanied by a rise in pressure in feedback signal line 42. Thischange in opposing pressures will cause spool 44 of flow control valveto shift to the left, to substantially reduce or cut offany output flowinto supply line 26b, thereby diverting most or all of the flow frominput supply line 26a to motor supply in line 32, where the demand hasbeen indicated to be. The drop in flow from flow control valve 16a intoline 26b will necessarily be reflected in a drop in flow through returnline 30 and demand sensing orifice 22. The resulting reduction inpressure drop across orifice 22 will shift piston 68 and pump demandvalve 20 back toward the right, which will in turn direct fluid fromline 28 to the left side of pump regulating motor 18 to start increasingthe output of pump 10 to meet the new demand called for by manualcontrol valve 140. As the output of pump [0 increases to meet thisdemand. the flow rate through line 26a, across spool 44, through line32, and across spool 54 to port 56 will increase. The increasing flowrate across spool 54 will cause a correspondingly increased pressuredrop thereacross. which pressure drop will be reflected by an increasingdifference in the pilot pressures applied to the opposite ends of spool44. The increasing difference will act to oppose spring 46, to graduallyshift spool 44 back to the right, thus redistributing the flow from line260 so that less goes to line 32 and more is diverted downstream to line26b. The resulting increase in flow to lines 26b, 26c and 30 will startincreasing the pressure drop across demand sensing orifice 22. This inturn will cause a leftward stroke ofpiston 68, to reduce the fluid flowto the left chamber of pump regulating motor 18 to stop the strokethereof and to signal pump 10 to maintain its existing output rate inview of the satisfied demand at hydraulic motor 120.

When motor 12a has completed its stroke, the termination of flow acrossspool 54 will restore spool 44 to its zero demand condition. This inturn will maximize the flow rate through orifice 22, and cause piston 68to stroke all the way to the left to again bring the pump output down toits minimum level.

Thus it is evident from the foregoing explanation that demand sensingorifice 22 is supplied with fluid in line 30 whose flow rate isinversely proportional to the demand called for by manual control valve140. That is. when valve 14a is in its neutral position, or when theflow rate which it calls for is satisfied by the pump, there will be arelatively high rate of flow in line 30, whereas an unsatisfied demandwill mean that the flow control valve 16a will have sharply reduced orcut off the flow rate into line 30.

The relationship of flow control valves [60, 16b and 16c in seriesestablishes a priority sequence among hydraulic motors 12a, 12b and l2e.For example, since flow control valve I6!) is supplied with fluid fromline 26b only when there is no substantial demand for fluid called forby manual control valve Me, a simultaneous demand for fluid by bothmanual control valves 14a and 1411 will result in most if not all of theoutput of pump being directed to motor 12a, at the expense of motor 12b.Only as the demand at motor 12a becomes satisfied, as reflected by theincreased flow rate across spool 54, will flow control valve 16b and itsassociated manual control valve 14b begin to receive any substantialquantity of fluid. The same priority relationship necessarily alsoexists as to the furthermost downstream flow control valve 160. Thesystem of the present invention accordingly establishes a prioritysequence which favors each upstream flow control valve relative to thenext downstream flow control valve.

The system of the present invention is capable of continuously sensingthe total unsatisfied demand for fluid. Thus, if motor control valves14a and 14b and/or 14c are all set to positions calling for less thanmaximum flow to each of their respective motors, demand sensing orifice22 will sum these demands. This occurs because each of the flow controlvalves in question will divert a portion of the pump output to itsassociated manual control valve, thus decreasing the flow passed on tothe next downstream flow control valve. Thus, the flow rate in line isreduced identically whether all of the demand comes from one motor orwhether the total demand is divided among the several motors.

The output of pump 10 will therefore be continuously responsive to thetotal demand of the circuit, while providing a slight additional flow toassure operation of all of the valves even when there is no demand.

As will be understood by those skilled in the art, pump demand valve 20could alternatively be a spring loaded cylinder and a three-way pilotoperated valve, Furthermore, various accessory valves can be readilyincorporated with the present system, such as pressure relief valves,valves to limit the horsepower output of the pump so as to preventstalling of the engine, and so forth.

In addition to the advantages described above, the pressure compensatedflow control valves will give good metering characteristics and lowspool efforts, possibly eliminating the need for powered spools in somecircuits. Furthermore, in some circuits where it may be desirable tolimit the maximum flow to a given section. this can be accomplished bylimiting the spool travel ofthat section.

This invention may be further developed within the scope of thefollowing claims. Accordingly, the above specification is to beinterpreted as illustrative of only a single operative embodiment ofthis invention, rather than in a strictly limited sense.

I now claim:

1, In a hydraulic circuit having a variable displacement pump, a pumpdisplacement controlling device, a plurality of hydraulic motors and aplurality of motor control valves, each hydraulic motor having anassociated motor control valve for controlling the fluid flow to suchhydraulic motor, the improved pump control system comprising:

a plurality of series-connected flow control valves each having its owninput line and first and second output lines, said input line of theupstream most flow control valve being connected to the output of thepump, said first output line of each of said flow control valves servingas an input line to an associated one of said motor control valves andbeing continuously connected across such flow control valve to the inputline of such flow control valve,

said second output line of each of said flow control valves beingconnected in series with the input line of the next downstream flowcontrol valve;

feedback singal means interconnecting each of said motor control valvesto its associated flow control valve and operable to sense the flow rateand flow demand through such motor control valve and to position theassociated flow control valve to reduce flow from the input line to thesecond output line of such flow control valve when the flow demanded bysuch motor control valve exceeds the flow rate therethrough, and toincrease the flow from said input line to said second output line as theflow rate through such motor control valve catches up with the demand,thereby establishing a fluid supply priority among said flow controlvalves and their associated motor control valves which favors eachupstream motor control valve relative to the next downstream motorcontrol valve;

said second output line of the downstream-most of said series-connectedflow control valves being connected to a flow demand-sensing device,said flow demand sensing device being connected to the pump displacementcontrolling device and being responsive to the flow rate in said secondoutput line of said downstream-most flow control valve to signal thepump displacement controlling device to control pump displacement ininverse proportion to said flow rate. which flow rate is inverselyproportional to the sum of the combined unsatisfied flow demand of allof said motor control valves.

2. An improved hydraulic control system for control ling the output of avariable displacement pump comprising:

a pump controlling hydraulic motor for varying the displacement of thepump. a pump control valve having an input line supplied with fluid fromthe pump and an outlet line leading to said pump controlling motor toactivate said motor to control the pump displacement according to theposition of said pump control valve, said pump control valve beingnormally biased to a minimum pump displacement producing position;

a flow demand sensing device connected to said pump control valve andresponsive to the fluid flow rate in a demand signal line flowingthrough said sensing device to cause said pump control valve to increasethe pump displacement in response to de creasing flow rate in saiddemand signal line, whereby pump displacement is inversely proportionalto the flow rate in said demand signal line:

a second hydraulic motor and a second motor control valve forcontrolling the flow of fluid thereto;

a third hydraulic motor and a third motor control valve for controllingthe flow of fluid thereto;

first and second flow control valves.

said first flow control valve having an input line and first and secondoutput lines, said input line being connected to the output line of thepump, said first output line continuously supplying fluid to said secondmotor control valve, and said second output line selectively supplyingfluid to said second flow control valve;

said second motor control valve including a valve element controllingthe communication between said first output line of said first flowcontrol valve and said second motor;

feedback signal means interconnecting said first flow control valve andsaid second motor control valve and operable to sense the flow ratedemanded by said second motor control valve and to sense the flow rateacross said valve element, and further operable to position said firstflow control valve to reduce flow from said input line to said secondoutput line when the flow demanded by said second motor control valveexceeds the flow rate therethrough, and to increase flow from said inputline to said second output line as the flow rate through said secondmotor control valve catches up with the demand;

said second flow control valve having an input line receiving all of theflow from said second output line of said first flow control valve andbeing sup plied with fluid only to the degree that said first flowcontrol valve directs fluid to the second output line thereof as theflow rate across said valve element ofsaid second motor control valvecatches up with the demand. and said second flow control valve furtherhaving first and second output lines, said first output line of saidsecond flow control valve continuously supplying fluid to said thirdmotor control valve, said second output line of said second flow controlvalve selectively supplying fluid to said demand signal line;

said third motor control valve having a valve element controlling thecommunication between said first output line of said second flow controlvalve and said third motor;

feedback signal means interconnecting said second flow control valve andsaid third motor control valve and operable to sense the flow ratedemanded by said third motor control valve and to sense the flow rateacross said valve element thereof, and further operable to position saidsecond flow control valve to reduce flow from said input line to saidsecond output line when the flow demanded by said third motor controlvalve exceeds the flow rate therethrough. and to increase flow from saidinput line to said second output line as the flow through said thirdmotor control valve catches up with the demand;

whereby the flow rate in said demand signal line is inverselyproportional to the sum of the combined unsatisfied flow demands of saidsecond and third motor control valves.

1. In a hydraulic circuit having a variable displacement pump, a pumpdisplacement controlling device, a plurality of hydraulic motors and aplurality of motor control valves, each hydraulic motor having anassociated motor control valve for controlling the fluid flow to suchhydraulic motor, the improved pump control system comprising: aplurality of series-connected flow control valves each having its owninput line and first and second output lines, said input line of theupstream most flow control valve being connected to the output of thepump, said first output line of each of said flow control valves servingas an input line to an associated one of said motor control valves andbeing continuously connected across such flow control valve to the inputline of such flow control valve, said second output line of each of saidflow control valves being connected in series with the input line of thenext downstream flow control valve; feedback singal meansinterconnecting each of said motor control valves to its associated flowcontrol valve and operable to sense the flow rate and flow demandthrough such motor control valve and to position the associated flowcontrol valve to reduce flow from the input line to the second outputline of such flow control valve when the flow demanded by such motorcontrol valve exceeds the flow rate therethrough, and to increase theflow from said input line to said second output line as the floW ratethrough such motor control valve catches up with the demand, therebyestablishing a fluid supply priority among said flow control valves andtheir associated motor control valves which favors each upstream motorcontrol valve relative to the next downstream motor control valve; saidsecond output line of the downstream-most of said seriesconnected flowcontrol valves being connected to a flow demandsensing device, said flowdemand sensing device being connected to the pump displacementcontrolling device and being responsive to the flow rate in said secondoutput line of said downstream-most flow control valve to signal thepump displacement controlling device to control pump displacement ininverse proportion to said flow rate, which flow rate is inverselyproportional to the sum of the combined unsatisfied flow demand of allof said motor control valves.
 2. An improved hydraulic control systemfor controlling the output of a variable displacement pump comprising: apump controlling hydraulic motor for varying the displacement of thepump, a pump control valve having an input line supplied with fluid fromthe pump and an outlet line leading to said pump controlling motor toactivate said motor to control the pump displacement according to theposition of said pump control valve, said pump control valve beingnormally biased to a minimum pump displacement producing position; aflow demand sensing device connected to said pump control valve andresponsive to the fluid flow rate in a demand signal line flowingthrough said sensing device to cause said pump control valve to increasethe pump displacement in response to decreasing flow rate in said demandsignal line, whereby pump displacement is inversely proportional to theflow rate in said demand signal line; a second hydraulic motor and asecond motor control valve for controlling the flow of fluid thereto; athird hydraulic motor and a third motor control valve for controllingthe flow of fluid thereto; first and second flow control valves; saidfirst flow control valve having an input line and first and secondoutput lines, said input line being connected to the output line of thepump, said first output line continuously supplying fluid to said secondmotor control valve, and said second output line selectively supplyingfluid to said second flow control valve; said second motor control valveincluding a valve element controlling the communication between saidfirst output line of said first flow control valve and said secondmotor; feedback signal means interconnecting said first flow controlvalve and said second motor control valve and operable to sense the flowrate demanded by said second motor control valve and to sense the flowrate across said valve element, and further operable to position saidfirst flow control valve to reduce flow from said input line to saidsecond output line when the flow demanded by said second motor controlvalve exceeds the flow rate therethrough, and to increase flow from saidinput line to said second output line as the flow rate through saidsecond motor control valve catches up with the demand; said second flowcontrol valve having an input line receiving all of the flow from saidsecond output line of said first flow control valve and being suppliedwith fluid only to the degree that said first flow control valve directsfluid to the second output line thereof as the flow rate across saidvalve element of said second motor control valve catches up with thedemand, and said second flow control valve further having first andsecond output lines, said first output line of said second flow controlvalve continuously supplying fluid to said third motor control valve,said second output line of said second flow control valve selectivelysupplying fluid to said demand signal line; said third motor controlvalve having a valve element controlling the communication between saidfirst output line of said second flow control valve anD said thirdmotor; feedback signal means interconnecting said second flow controlvalve and said third motor control valve and operable to sense the flowrate demanded by said third motor control valve and to sense the flowrate across said valve element thereof, and further operable to positionsaid second flow control valve to reduce flow from said input line tosaid second output line when the flow demanded by said third motorcontrol valve exceeds the flow rate therethrough, and to increase flowfrom said input line to said second output line as the flow through saidthird motor control valve catches up with the demand; whereby the flowrate in said demand signal line is inversely proportional to the sum ofthe combined unsatisfied flow demands of said second and third motorcontrol valves.